Comparison of whole plant and detached leaf screening techniques for identifying anthracnose resistance in strawberry plants

Authors: Miller Butler, Melinda; Smith, Barbara; Babiker, Ebrahiem; KREISER, BRIAN - University Of Southern Mississippi; BLYTHE, EUGENE - Mississippi State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2018
Publication Date: 9/13/2018
Citation: Miller Butler, M.A., Smith, B.J., Babiker, E.M., Kreiser, B.R., Blythe, E.K. 2018. Comparison of whole plant and detached leaf screening techniques for identifying anthracnose resistance in strawberry plants. Plant Disease. 102(11):2112-2119. https://doi.org/10.1094/PDIS-08-17-1138-RE.
DOI: https://doi.org/10.1094/PDIS-08-17-1138-RE

Interpretive Summary: Strawberries are host for many plant disease pathogens, and anthracnose, caused by pathogenic fungi in the Colletotrichum genus, is one of the more destructive diseases. Strawberry breeding programs generally require many years to develop disease resistant cultivars that can be released to commercial growers. Traditionally whole strawberry plants are inoculated with a pathogenic fungus to determine plant resistance, but often valuable breeding lines are lost due to these inoculations which slowed the breeding program. Our research used detached leaves, instead of whole plants, to decrease the time between inoculation and identification of disease resistance and to eliminate the possibility of killing plants. We tested 81 germplasm lines by inoculating whole plants and detached leaves from the same population with pathogenic fungal isolates known to cause anthracnose in strawberry. Whole plants were rated for disease severity at 30 days after inoculation and detached leaves were rated at 5 days after inoculation. The association between the whole plant disease severity rating and the detached leaf disease severity was positive. This research indicates a strawberry detached leaf inoculation assay can reliably and quickly determine the degree of anthracnose resistance in strawberry plants. The use of detached leaves for anthracnose resistance testing will shorten the disease rating process, remove the possibility of losing valuable breeding stock that may have other positive horticultural traits, and ultimately provide strawberry growers with anthracnose resistant cultivars.

Technical Abstract: Anthracnose is a destructive disease of strawberry caused by several Colletotrichum species including C. acutatum, C. fragariae, and C. gloeosporioides. Identification of anthracnose resistant strawberry germplasm has commonly relied on inoculation of whole plants with isolates of these pathogens. In this study, whole plants and detached leaves from 81 germplasm lines were inoculated with a conidial suspension of isolates of C. fragariae and C. gloeosporioides, incubated in the dark at 30 °C, 100% relative humidity, for 48 hours, and assessed for disease severity based on symptoms on inoculated petioles and leaves. The correlation between the disease severity ratings of the whole plants rated 30 days after inoculation and detached leaves rated 5 days after inoculation was determined. Based on leaf symptoms and petiole lesions, the association between the whole plant leaf disease severity rating (DSR) and detached leaf DSR was positive (rp = 0.70) and (rp = 0.66) respectively. A post hoc Tukey’s test showed that the whole plant DSR means and the detached leaf DSR means for each resistance category differed significantly at p < 0.05. This research indicates a strawberry detached leaf assay can reliably and quickly determine the degree of resistance of strawberry germplasm to anthracnose.